1. Field of the Invention
The present invention relates to a touch panel mainly used for operating various kinds of electronic equipments and a method of detecting a press operation position thereon.
2. Background Art
Recently, various kinds of electronic equipments such as a portable telephone and an electronic camera have advanced in functions and become diversified. Along with this, the number of equipments in which a light-transparent touch panel is mounted on the front surface of a liquid crystal display device or the like is increasing. A user operates by pressing a touch panel with a finger thereof, a pen, or the like, while viewing the indication on a display device at the back of the touch panel. According to this operation, various functions of equipment can be switched from one function to another. Such a conventional touch panel is described with reference to FIG. 19. FIG. 19 is a sectional view showing a conventional touch panel. Note here that the drawing is shown in an enlarged size partially so that the configuration can be understood easily.
This touch panel includes film-shaped light-transparent upper substrate 1, light-transparent lower substrate 2 made of glass or the like, frame-shaped spacer 5 disposed on the inner edge of the outer periphery of upper substrate 1 and lower substrate 2 therebetween. Light-transparent upper conductive layer 3 is formed in a substantially rectangular shape on a substantially entire surface of the bottom surface of upper substrate 1. Light-transparent lower conductive layer 4 is formed on a substantially entire surface of the top surface of lower substrate 2. A plurality of dot spacers (not shown) made of insulating resin are formed on the top surface of lower conductive layer 4 with a predetermined interval. A pair of upper electrodes (not shown) are formed on both ends of upper conductive layer 3, and a pair of lower electrodes (not shown) are formed on both ends of lower conductive layer 4 in the direction perpendicular to the upper electrodes.
On the top and bottom surfaces of spacer 5, an adhesive agent (not shown) is coated. Upper substrate 1 and lower substrate 2 are attached together at their outer peripheries with the adhesive agent. Upper conductive layer 3 and lower conductive layer 4 face each other with a predetermined gap therebetween, and thus the touch panel is formed. The thus formed touch panel is disposed on the front surface of a display device and mounted on electronic equipment. The pairs of the top and lower electrodes are electrically connected to an electronic circuit (not shown) of the equipment.
When a user presses a top surface of upper substrate 1 to operate the touch panel by a finger, a pen, or the like in response to an indication on the display device at the back of the touch panel, upper substrate 1 bends downward, causing upper conductive layer 3 at the pressed place to be brought into contact with lower conductive layer 4. The electronic circuit applies a voltage to the upper electrodes and the lower electrodes sequentially. The electronic circuit detects the pressed place by a ratio of the voltages between the respective pair of electrodes, and thereby switches various functions of equipment.
That is to say, a user presses the top surface of upper substrate 1 in a position on a desired menu in a state in which a plurality of menus, or the like, are displayed on the display device at the back of the touch panel. The electronic circuit detects the operated position by a ratio of the voltage between the upper electrodes and the voltage between the lower electrodes, thereby selecting a desired menu from a plurality of menus.
As mentioned above, the pair of upper electrodes are provided on both ends of the substantially rectangular-shaped upper conductive layer 3 provided on the bottom surface of upper substrate 1. The pair of lower electrodes are provided on both ends in the direction perpendicular to the upper electrodes of similarly substantially rectangular-shaped lower conductive layer 4 on the top surface of lower substrate 2. The electronic circuit detects the pressed place by a ratio of the voltages between the respective pair of electrodes. Therefore, the electronic circuit can detect only one pressed position. For example, when a user presses the position shown by arrow M by one finger and simultaneously presses the position shown by arrow N by another finger, the electronic circuit cannot detect these two pressed positions simultaneously.
In order to detect the pressed positions in such a state, for example, a touch panel has been devised in which upper conductive layer 3 and lower conductive layer 4 are formed of a plurality of conductive layers in a substantially belt shape instead of a substantially rectangular shape and they are allowed to cross in the direction perpendicular to each other and to face each other with a predetermined gap therebetween. By applying a voltage to these conductive layers sequentially, a plurality of pressed positions can be detected. In this case, the formation of a touch panel generally needs several to several tens of conductive layers although it depends on the size of a touch panel.
In the case where a plurality of top and lower conductive layers are provided in this way, several tens of top and lower electrodes are required for the connection from respective conductive layers to an electronic circuit. Therefore, the entire outer shape becomes larger. Moreover, since it is necessary to detect a pressed position by sequentially applying a voltage to all of the electrodes, it takes a long time to detect a position. The connection to an electronic circuit and arithmetic processing for detecting a position become complicated.